A turning tool used in grooving operations typically comprises a tool body and a detachable cutting insert clamped in the tool body by the use of tightening means. Such a tool body comprises a fitting member, such as a shaft, for fixing the tool onto a machine, such as a computer numerical control (CNC) machine or a turning lathe. It further comprises an upper and a lower clamping member on which inner seating surfaces are provided, defining an intermediate gap. The cutting insert is inserted in the intermediate gap between the seating surfaces and the tightening means is thereafter used to secure the cutting insert in the gap, with a rake face directed upward. For some grooving tools, including some face grooving tools, the tool body commonly has a major part of each inner seating surface extending transversely to a major extension of the fitting member, so that a major cutting edge of the cutting insert thereby extends in parallel to a long axis of the fitting member. Such face grooving tools commonly have a lower clamping member, which has a curvature corresponding to a predetermined groove diameter range. The cutting insert is thereby configured to cut a circular groove in a front end of a rotating work piece, which groove extends in a plane which is parallel to the major extension of the work piece, or extends parallel to a rotation axis of the work piece. Such a tool, having a fitting member in the form of a shank, is referred to as a 90° style shank tool. 90° style shank tools for face grooving are used in external face grooving where the machine in which the fixing member is fixed is configured such that 90° style shank tools are most suitable. For example, a tool revolver in a machine may be configured such that tools can only be fixed perpendicularly to the rotation axis of the work piece in which a groove is to be machined.
The tightening means may e.g. be in the form of a screw. By tightening the screw, the inner seating surfaces of the clamping members are pressed toward each other and thereby hold the cutting insert in a fixed position between the inner seating surfaces. In order to be able to move the inner seating surfaces of the clamping members toward one another to secure the cutting insert in the intermediate gap between the inner seating surfaces, a hinge joint around which the clamping members are turnable is commonly provided.
Tool bodies may advantageously be integrally formed in a unitary piece, comprising both the fitting member and the two clamping members. This type of tool body has an increased rigidity in comparison with tool bodies comprising separate parts, such as a tool body having a separate head end comprising the clamping members and a back end comprising the fitting member. Furthermore, the dimensional accuracy of the machined grooves is improved. The hinge joint is in this type of tool bodies in the form of an elastic material portion, which can be elastically deflected. Furthermore, tool bodies which are integrally formed in a unitary piece can be used effectively, e.g. with reduced leakage or pressure reduction, where a coolant fluid is supplied from the fitting member to one or both of the clamping members such that one or more coolant outlets are formed as close as possible to the active cutting edge, in order to effectively reduce the temperature of the cutting insert and to improve the chip breaking.
In integrally formed tool bodies intended for face grooving operations, the hinge joint is, for ease of manufacture, usually formed such that it extends in parallel to a major extension of the inner seating surface. When a cutting insert is mounted in the tool body, its major cutting edge thus has an extension which is perpendicular to said hinge joint. When clamped by the seating surfaces, the inventors of the present invention have found that the cutting insert has a tendency to rotate slightly around its long axis, extending in parallel with the hinge joint. This leads to incorrect dimensions of grooves created using the tool, and also to defective side surfaces of those grooves. For example, the groove width may have a smaller width than the width of the major cutting edge of the grooving insert. To overcome this problem, a balancing screw is commonly used to balance the forces, or to reduce the rotation of the cutting insert. However, the balancing screw is difficult to adjust since it needs to be on a correct level with respect to the cutting insert. If not, the load on the cutting insert will be unevenly distributed. Upon machining, this creates stress concentration in the hinge joint and may ultimately lead to fracture. Further, a balancing screw and a hole for such a balancing screw give a higher manufacturing cost of the tool.